Pre-travel and overtravel are two commonly specified requirements for a switch. Pre-travel is the amount of movement of the switch actuator mechanism before switch changes its electrical state, i.e., the electrical state between the terminals of the switch changes. The electrical state between a pair of switch terminals is typically either an electrical open circuit or a short circuit. Overtravel is the amount of movement that the switch actuator is designed to accommodate after the switch changes state. The sum of pre-travel and overtravel is the total travel of the switch actuator.
The rise of terrorism in the world has created the need to secure and protect activities of a general commercial nature. One such need is that of securing shipping containers against unauthorized opening after the container has been readied and sealed for shipment. Electronic systems that utilize electrical switches are being designed to track and monitor containers with respect to unauthorized opening as the containers are in transit to their respective destinations. As there is a large embedded base of shipping containers, the switches for this application must be compatible with existing container designs and must be capable of withstanding rough treatment and operate flawlessly with different containers having rather large part tolerances. In one proposed application, it is contemplated that a door switch be mounted on each shipping container between the small space between the door and door jamb. For this application, the switch must be robust and possess particular pre-travel and overtravel requirements. While electrical switches exist in a myriad of shapes, sizes, and designs, no existing switch exists that can met the requirements of the shipping container application. Accordingly, providing a door switch for a system designed to detect unauthorized opening of shipping containers would be desirable.